The increasing demand for processed turkey and chickens, cut up chicken and poultry white meat in general, has raised the price of such cuts while at the same time creating a demand to find value-added uses for residual poultry parts such as wings, necks, thighs, backs and drumsticks. A substantial portion of these residual products become mechanically deboned poultry meat.
Mechanically deboned poultry meat (MDPM) is a finely comminuted paste that has mainly been used in the production of emulsion-type products like wieners and luncheon meats. Several constraints have limited its broader use: dark red color, small particle size (that results in poor texture properties) and short storage life.
The mechanical deboners most commonly used in the poultry industry can be classified in two groups: press-type and auger-type. These deboners are designed to accept raw or cooked materials and process as much as 6,000 lb/hr or as little as 500 lb/hr.
In the press-type deboners, bones with adhering meat are placed directly into the chamber of the machine without preliminary grinding or breaking. These deboners in general are batch producers, where a determined weight of meat and bones is fed into a thick-walled steel cylinder. A hydraulically-powered piston compacts the meat and bones under a pressure of 100 to 250 atm. Meat is forced through a set of microgrooves which the bones are unable to enter and are removed by the piston; examples of this kind of deboners are the Protecon and the Unilever.
Poultry processors in the United States and Europe predominantly use auger-type deboning machines, which can work on a one or two-stage continuous process. In the two-stage, the raw materials are first chopped into smaller portions after which the edible meat or soft tissue is separated from the bone via stainless steel screens (Yieldmaster) or via microgrooves (Paoli).
The one-stage auger deboners are the newest type on the market. In these deboners no preliminary grinding is required.
The recovered meat yields of auger-type deboners by weight of material fed, as reported by the manufacturers are 92% for whole fish; 50% for fish frames, 55% for lobster bodies, and 65% for whole poultry carcasses. A whole carcass gives a higher yield than just parts. However, the new one-stage auger-type Paoli deboner claims a yield of 60-75% in fryer necks and backs; 50-65% in poultry carcasses and 42-67% in turkey carcasses. The Beehive Rotatory Separator claims to achieve the following yields: turkey frames 65%, turkey necks 63%, and whole birds 75-89%, by weight.
The proximal composition of meats is affected by the mechanical deboning process. Part of the lipids and heme compounds of the bone marrow end up in the mechanically separated meat. The incorporation of these materials substantially increases the lipid fraction of the final product by diluting the fractions of other components. Reports on the proximal composition of mechanically deboned poultry meat vary widely from author to author; much of the variability relating to such factors as the age of the bird, bone to meat ratio, cutting methods, deboner settings, skin content, and protein denaturation (Froning, Food Technology, 9:50-63 (1976): Essary, J. Food Sci., 44:1070-1073 (1979).
The shearing forces present in the mechanical deboning process cause considerable damage to the cellular structure of the tissues. As a result, the product obtained from mechanical deboning is a very fine meat puree which lacks shape and texture. Poor texture properties in MDPM are related to the loss of the integrity of the myofibrils which are heavily fragmented during the deboning process. Schnell et al, Poultry Sci., 53:416-419 (1974) studied the ultrastructure of MDPM. Using a deboner with screen sizes of 0.1575, 0.1016 and 0.0508 centimeters it was found that a decrease in screen size caused a loss in the integrity of the myofibrils. In other words, the characteristic size of the myofibrils showed more damage when a smaller screen was used. Breaks occurred in the Z and M lines. Once broken, further structural disintegration occurred with the shearing forces that produced particles which were spherical or oval in shape. Valdehra and Baker, Food Tech., 24:42 (1970) reported that histologically, no intact muscle fiber has been observed in commercially deboned neck and back meats.
Studies by Satterlee et al, J. Food Sci., 36:979-981 (1971), and Froning et al, J. Food Sci., 38:279 (1973) which varied the skin percentage of broiler backs going into the deboner showed that as the skin percentage of the backs increased, the fat content of the MDPM increased. This increase in fat affected the percentage of protein, moisture and bone fractions in the final product as well. Results showed that most of the fat went into the edible product rather than into the bone residue; conversely, the protein collagen was mostly found in the bone residue. This showed that most of the skin protein did not pass through the deboner screen.
In order to maintain certain parameters of quality, the U.S. Department of Agriculture has ruled that mechanically deboned meat (MDM) has to have no less than 14% protein, no less than a 2.5 Protein Efficiency Ratio (PER) and no more than 30% fat (Federal Register, 1985).
Some of the recommended ways to increase or improve the texture and emulsifying characteristics of the MDM are achieved with the addition of hand deboned meat, structural protein fibers (soy protein), and other ingredients. The addition of intact meat fibers will impart better texture to the final product. In finished products such as meat rolls, meat balls and coarsely ground sausages, approximately 25% of the total ingredients has been structural protein fibers (Kumar et al, Avian Res., 67:108-115 (1983). A problem with structural protein fibers is that they impart a distinctive soy flavor at high levels.
The color of meat is influenced by several factors starting from animal husbandry practices to the final conditions under which the meat is displayed on the retail level. In general, the chemistry of the color in meat is primarily due to the muscle protein myoglobin. Differences in color can be measured using appropriate equipment; one such apparatus is the Hunterlab Color Difference Meter which measures color in foods. It defines color in terms of lightness (L); and two chromaticity dimensions--(a) from green to red and (b) from blue to yellow. Lightness values range from 100 to 0, where 100 represents perfect white and 0 strands for black. The chromaticity dimensions (a and b) give certain designations of color as follows: "a" measures red when positive, gray when zero, and green when negative; while "b" measures yellow when positive, gray when zero and blue when negative (Mackinney and Little, Color of Foods, AUI Pub. Co., Westport, Conn. 1962). From these values the hue angle (H.degree. ) and the saturation (S) can be calculated (MacDougall, Food Chem., 9:75-88 (1982)).
The pigments responsible for color of meat are heme pigments contained in the proteins myoglobin and hemoglobin.
In the structure of the heme pigment itself the chemical state of the cental iron present strongly influences the meats' color.
The iron in the heme group can be present in either a ferrous or oxidized ferric state. To maintain a desirable color in meat, myoglobin must remain in a ferrous form.
Several methods have been tried for the extraction and quantification of the heme pigments. Heme pigments are usually chemically converted to specific and more stable derivative for their measurement. Hornsey's method, J. Sci. Food and Agric., 7:534-540 (1956) transformed the heme t hematin and Warris' method Analyt. Biochem., 72:104-112 (1976) changed the heme into a cyanmet form developed from cyanide salts. Early experiments attempted to extract the heme pigments in meat with water washings. Studies by Poel, Am. J. Physiol., 156:44 (1949), and Fleming et al, J. Am. Sci., 19:1164-1171 (1960) have indicated that water did not remove the pigments completely. Watson, Biochem. J., 29:2114-2120 (1935) tried several phosphate buffers and he found that alkaline phosphate buffers were helpful in removing the pigments, but their filtrate was turbid. Therefore, he was unable to make accurate readings of the pigment concentration. However, when acid phosphate buffers were used, they produced a clearer filtrate. He finally recommended two washings with a 0.067M phosphate buffer at a pH of 6.5 to remove the heme pigment from meat.
Tested methods for the extraction of heme pigments include DeDuve's method, Acta Chemica. Scand., 2:264 (1948) and Hornsey's method, supra (1956). In DeDuve's method, the pigment was removed by using a 0.01N acetate buffer at a pH of 4.5. In this method the extract was clear; however, 5 to 30% of the total pigment remained unextracted from the muscle. In Hornsey's method several acetone/water ratios were used to remove the heme pigments. In this procedure the ratio of acetone/water was found to be critical in the amount of pigment washed out. Maximum extraction was obtained at a 4:1 acetone/water ratio. The addition of hydrochloric acid in the acetone solvent converted the heme pigments into a stable hematin derivative, which then allowed measurements to be recorded. The same findings were reported by Hagerdal et al, J. Food Sci, 42:1258-1263 (1977).
Warris, J. Food Tech., 14:75-80 (1979) investigated the pigment removal using a phosphate buffer with the further addition of sodium cyanide and potassium ferricyanide. These compounds converted the heme pigments to a stable cyanmet form. After that, readings on the clarified solutions were made at 540 nm to determine the total pigment extracted. In 1979 Warris tried various buffers having different values of pH to remove heme groups. He concluded that the best extracting buffer was a 0.04M phosphate buffer at a pH of 6.8. Moreover he proved once again that water and buffers of a low pH resulted in the inability of up to 45% of the pigments to be extracted. According to Warris the maximum pigment extraction was achieved by buffers having a pH above 6.8 but the clarification of the solutions caused some difficulties. All extracts obtained were impossible to clean by centrifugation. Unlike previous studies which used two washings, he demonstrated that a single extraction was sufficient to remove all of the soluble pigment. Finally, he established that the pH for the extracts was lower than the original buffer solution used due to the buffering capacity of meat.
Due to most consumers' preference for white meat in poultry, some experiments have been done recently aimed at obtaining white meat from red parts. The possible use of bleached red muscle in white meat-products will greatly decrease costs and utilize expensive wasted protein. Ball et al, Abst. of Papers, 73rd Ann. Meet., Poultry Sci. Assoc., Ont. Canada (1984) tried different extracting media such as: tap water, sodium bicarbonate (pH 8.45), and sodium acetate (pH 5.25) to remove pigments from the thigh meat of broilers. They reported that by washing the meat in these different solutions the pigment was reduced from 73 to 88%, depending on the specific chemical applied. In addition, their study indicated that the washing step affected nutrient levels; niacin was lost at a level of 54.7 .mu.g/g and thiamine at 0.88 mg/g. A sensory study carried out by the above authors showed that the washed tissue was judged in color between breast meat and thigh meat.
Acton, (through personal communication) (1984), has been using oxidizing agents to bleach meat. These three agents are: hydrogen peroxide, sodium bisulfite, and ascorbic acid. The sodium bisulfite solution left a sulfur-like taste in the washed product, which was not found in the meat treated with hydrogen peroxide or ascorbic acid. Further study is indicated in the use of oxidizing agents, especially when applied to MDPM because of the possible acceleration of lipid oxidation causing off-flavors, or composition damage of amino acids in the final product. Additional research is required for evaluating the effect of washing and bleaching agents in the overall nutritional quality and storage stability of the final products.
The possibility of using mechanical deboners in foods was first tested in the fish industry. Similarly to MDPM, the mechanically deboned fish has found broad utilization in several food products. In Japan, the mechanically deboned fish has been extensively used in the elaboration of kamaboko products and surimi. Kamaboko, used as a generic term, identifies different rubbery and sponge-like fish cakes (Okada et al, Marine Fisheries Rev., 35:1-6 (1973)). Kamboko products have enjoyed a wide popularity in Japan for many centuries; documents from the 15th century mention the methods used in its preparation.
The process of kamaboko involves the grinding of washed fish muscle with starch, sugar, and salt to form a sticky paste. The paste then can be boiled, steamed, broiled or deep-fried. Kamaboko is called by different names depending on the type of cooking, shape and ingredients of the final product.
At the Hokkaido Fisheries Laboratory, in 1959, Nishiya and Takeda developed a process for preparing surimi, a semi-processed fish protein that has revolutionized the kamaboko industry. The initial steps of the surimi process are similar to those of kamaboko: the raw fish has the head and internal organs removed, and then it is filleted, minced, and washed. After that the water is extracted and the resultant paste is strained. However, unlike kamaboko method, certain additives are incorporated in the straining step of surimi production. The surimi paste is shaped in rectangular blocks, packaged, and frozen. The additives added during straining cause the muscle proteins to retain their functional properties longer during frozen storage.
The fish meat is collected and mixed with cold water (0.degree. C.) 7-8 times its volume. After a short mixing, the flesh is allowed to settle and the supernatant is discarded. The washing step removes unpleasant fishy odors, fat, blood, and flesh pigments. It also removes water soluble proteins, thus improving the elasticity or "ashi" of the final product (Okada et al, supra, 1973). This washing step is repeated 3 to 5 times. During the final washing the water is removed from the minced fish by the use of a screw press or a centrifuge. The final moisture content is 84-86%. The number of washing steps and the volume of water used in each step will vary according to the species of fish, the initial condition of the raw material, the type of washing unit utilized, and the quality of surimi desired (Lee, Food Tech., 38:69-80 (1984)).
There is a major difference in procedures used for processing surimi on shore and that manufactured at ship factories. Due to the limitations in the amount of fresh water available at a ship factory, the washing step is only done once and the ratio of fish meat-water is 1:3 or 1:4..sup.2
The following references which relate to meat process are of background interest:
Valdehra et al, Food Tech., 24:42-55 (1970), reviews the mechanism of heat initiated binding of poultry meat; U.S. 3,076,713, to Maas, relates to mechanically working the surface of meat pieces until a creamy, tacky exudate forms and then pressing the pieces together; Schmidt et al, Recent Advances in the Chemistry of Meat, pp 231-245 (1984), reviews in detail various aspects of meat binding including mechanical treatment which causes both increased fiber description and the release of binding proteins; Siegel et al, J. Food Sci., 43:331-333 (1978), compares massaging meat surfaces and various chemical treatments on the quality of composite hams; Maesso et al, J. Food Sci., 35:440-443 (1970), studies the effects of physical and chemical treatments on binding of poultry meat pieces. Beating enhanced binding in all cases; Maesso et al, Poultry Sci., 44:697-700 (1970), looks at vacuum, pressure, pH and meat type as they affect binding; U.S. Pat. No. 3,499,767, to Schlamb, describes forming small pieces of poultry into large pieces by breaking the surface cells of the small pieces by mechanical action and binding through the action of released soluble proteins; Marshall, "New Marketable Poultry and Egg Products 6. Chicken Franks" A.E. Res. 57, January 1961, Cornell Univ., shows the formula for chicken franks and reports market studies; U.S. Pat. No. 1,427,438 to Brickman, shows using processed pork rind to hold two pieces of pork together; U.S. Pat. No. 1,503,864, to Vogt, shows making a boneless boiled ham; U.S. Pat. No. 2,766,122, to George, relates to recovering and using the edible flavor portion of a turkey; U.S. Pat. No. 3,036,922, to Saverslak, relates to the use of gluten as a poultry meat binder; U.S. Pat. No. 3,173,795, to Torr, relates to using poultry skin comminuted to fibriform consistency as a matrix to bind meat pieces; Turner et al, J. Food Sci., 44:1443-1446 (1979), studies the action of myosin as a meat binder; Siegel et al, J. Food Sci., 44:1129-1131 (1979), studies the action of myosin as a meat binder; Solomon et al, J. Food Sci., 45:283-287 (1980), looks at the effect of vacuum and mixing time on processing beef; MacFarlane et al, J. Food Sci., 42:1603-1605 (1977), studies the action of various specific proteins on meat binding; U.S. Pat. No. 3,595,682 to Lind et al, relates to a turkey roll employing turkey skin as an outer casing; U.S. Pat. No. 3,911,154 to Weatherspoon, teaches a composite meat product comprising a unitary outside stuffed with a mixture of meat ingredients the inside of the unitary cover is treated with salt and mechanically tenderized; U.S. Pat. No. 4,309,450 to Seibert, describes a seafood product from a composite exudate: U.S. Pat. No. 4,377,597 to Shapiro et al, describes a restructed meat product from meat chunks and alongated thin strips of meat; U.S. Pat. No. 3,268,339 to Torr, describes a poultry product made by mixing a fibriformed mass and chunks of raw meat to form a coherent mass. The fibriformed mass comprises skin preferably mixed with dark meat.